One proposed engine misfire detection apparatus adopts a specific criterion level lower than a standard criterion level for detection of a misfire of an internal combustion engine during warm-up of a catalyst included in an exhaust emission control unit for catalytic conversion of the exhaust emission from the internal combustion engine (see, for example, Patent Document 1). The proposed apparatus detects a misfire of the internal combustion engine during the catalyst warm-up time when an average rotation speed variation of the internal combustion engine exceeds the specific criterion level lower than the standard criterion level.
[Patent Document 1] Japanese Patent Laid-Open Gazette No. 2002-4936